Closed loop module control for communication based on signal quality

ABSTRACT

The present invention is directed to communication systems and methods. According to an embodiment, a receiving optical transceiver determines signal quality for signals received from a transmitting optical transceiver. Information related to the signal quality is embedded into back-channel data and sent to the transmitting optical transceiver. The transmitting optical transceiver detects the presence of the back-channel data and adjusts one or more of its operating parameters based on the back-channel data. There are other embodiments as well.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S.application Ser. No. 15/411,914, filed Jan. 20, 2017, commonly assignedand incorporated by reference herein for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

NOT APPLICABLE

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

NOT APPLICABLE

BACKGROUND OF THE INVENTION

The present invention is directed to communication systems and methods.

Over the last few decades, the use of communication networks exploded.In the early days of the Internet, popular applications were limited toemails, bulletin board, and mostly informational and text-based web pagesurfing, and the amount of data transferred was usually relativelysmall. Today, Internet and mobile applications demand a huge amount ofbandwidth for transferring photo, video, music, and other multimediafiles. For example, a social network like Facebook processes more than500 TB of data daily. To move a large amount of data, opticalcommunication networks are often used.

With high demand for communication networks came high demand for qualitynetworking devices. In high-speed communication systems, havingoptimized optical transceivers can meaningfully improve performance. Forexample, various parameters of optical transmitter, such as biasvoltages for modulator and laser devices, can be adjusted and optimizedin a communication system for improved performance.

Over the past, there have been various techniques for optimizingparameters and settings for optical transceivers. Unfortunately,existing techniques are inadequate for reasons explained below. Improvedmethods and systems for optimizing optical communication devices aredesired.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to communication systems and methods.According to an embodiment, a receiving optical transceiver determinessignal quality for signals received from a transmitting opticaltransceiver. Information related to the signal quality is embedded intoback-channel data and sent to the transmitting optical transceiver. Thetransmitting optical transceiver detects the presence of theback-channel data and adjusts one or more of its operating parametersbased on the back-channel data. There are other embodiments as well.

According to an embodiment, the present invention provides an opticaltransceiver apparatus, which includes an optical receiver for convertingincoming optical signals to incoming electrical signals. The apparatusincludes a digital signal processor (DSP) that is configured to analyzethe incoming electrical signals and to generate a first signal qualityvalue characterizing the incoming electrical signals. The apparatus alsoincludes a forward-error correction (FEC) module that is configured toprocess the incoming electrical signal and to generate a second signalquality value characterizing an error rate associated with the incomingelectrical signals. The apparatus further includes a control module thatis configured to generate back-channel data based at least on the firstsignal quality value and the second signal quality value. The controlmodule further is configured to insert the back-channel data to anoutgoing data stream. The apparatus also includes an optical transmitterfor generating output optical signals based on the outgoing data stream.

According to another embodiment, the present invention provides anoptical communication system. The system includes an opticalcommunication link. The system also includes a first transceivercomprising a first control module and a first optical transmitter. Thesystem additionally includes a second transceiver comprising a secondcontrol and a second optical transmitter. The second transceiver isconfigured to send data to the first transceiver. The first transceiveris configured to process a first data stream received from the secondtransceiver and to detect a first back channel data. If the firsttransceiver detects the first back channel data, the first transceiveris configured to determine signal characteristics information associatedwith the first data stream and insert the signal characteristicinformation into a second back channel data. The second back channeldata is embedded in a second data stream. The second transceiver isconfigured to process the second data stream received from the firsttransceiver. The second transceiver is configured to detect the secondback channel data and adjusts one or more operating parameters based onthe signal characteristic information.

According to yet another embodiment, the present invention provides amethod for optimizing optical communication. The method includestransmitting a first data stream from a first optical transceiver to asecond optical transceiver via an optical communication link. The methodalso includes detecting a first back-channel data segment at the firstdata stream by the second optical transceiver. The method additionallyincludes determining a first set of measurements associated with thefirst data stream by the second optical transceiver. The methodadditionally includes generating a second back-channel data by thesecond optical transceiver. The second back-channel data include thesecond set of measurements. The method also includes inserting thesecond back-channel data to a second data stream by the second opticaltransceiver. The method additionally includes transmitting the seconddata stream from the second optical transceiver to the first opticaltransceiver. The method further includes detecting the secondback-channel data by the first optical transceiver. The method alsoincludes determining a first set of adjustments by the first opticaltransceiver based on the first set of measurements. The method furtherincludes applying the first set of adjustments to an optical transmitterby the first optical transceiver.

It is to be appreciated that embodiments of the present inventionprovide many advantages over conventional techniques. Among otherthings, by measuring actual signal characteristics by a receivingoptical transceiver of the data communication path, adjustments made bya transmitting optical transceiver improve data transmission qualitybetter than existing techniques, where typically one-time factorysettings are applied to optical transceivers. For example, adjustmentssuch as wavelength control may be specific to the optical link andactual operating conditions (e.g., temperature, interference, etc.),which are information unavailable when optical transceivers weremanufactured. It is therefore advantageous for the closed looptechniques provided by the present invention to use these informationand hence improved performance.

Embodiments of the present invention can be implemented in conjunctionwith existing systems and processes. For example, the back-channel datacan be implemented to be compatible with existing communicationprotocols. Back-channel data are used by optical transceivers that arepreconfigured to use them, and optical transceivers that are notconfigured to use the back-channel data may simply ignore them. Inaddition, optical transceivers according to embodiments of the presentinvention can be manufactured using existing manufacturing equipment andtechniques. In certain implementations, existing optical transceiverscan be upgraded (e.g., through firmware update) to take advantage of thepresent invention. There are other benefits as well.

The present invention achieves these benefits and others in the contextof known technology. However, a further understanding of the nature andadvantages of the present invention may be realized by reference to thelatter portions of the specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following diagrams are merely examples, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize many other variations, modifications, and alternatives.It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this process andscope of the appended claims.

FIG. 1 is a simplified diagram illustrating optical transceiveraccording to an embodiment of the present invention.

FIG. 2 is a simplified diagram illustrating an encoded data frameaccording to embodiments of the present invention.

FIG. 3 is a simplified diagram illustrating an optical transmitter withback-channel data control according to embodiments of the presentinvention.

FIG. 4 is a simplified diagram illustrating an optical receiver 400according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to communication systems and methods.According to an embodiment, a receiving optical transceiver determinessignal quality for signals received from a transmitting opticaltransceiver. Information related to the signal quality is embedded intoback-channel data and sent to the transmitting optical transceiver. Thetransmitting optical transceiver detects the presence of theback-channel data and adjusts one or more of its operating parametersbased on the back-channel data. There are other embodiments as well.

Most optical communication modules have some form of internal controlsystems to maintain the optical performance. For example, typicalcontrol parameters include optical power, wavelength, extinction ratio,and/or others. However, in most cases, conventional techniques for thetransmitting optical module to maintain these parameters rely on proxymeasurements. For example, transmitted optical power may be measured bya tap and photodiode, or extinction ratio may be inferred from amodulator bias. Unfortunately, these conventional techniques areinadequate. A difficulty is that these proxy measurements may notrepresent the actual transmission characteristics, and as a result thetransmitting optical path is not optimized.

In optical communication, another difficulty is that in an optical linesystem (including fiber optics, amplifiers,multiplexers/de-multiplexers, dispersion compensation, etc.), optimaltransmission parameters may not be constant and may in fact change dueto the line equipment or conditions. This may render the transmissionparameters even farther from optimal.

It is to be appreciated that embodiments of the present inventionprovide advantages over existing techniques. More specifically,embodiments of the present invention make use of digital signalprocessors (DSP) and forward error correction (FEC) modules on theoptical receive path. The inclusion of a DSP and FEC on the opticalreceive path within the module itself allows the receiving side todetermine the quality of the incoming optical signal. Additionally,embodiments of the present invention provide an advanced FEC encodingthat includes the ability to place additional digital informationalongside the transmitted data (“back-channel”), thereby allowing thereceive-side module to inform the transmitting-side module of thecurrent signal integrity.

With DSP/FEC and advanced FEC encoding working together, a closed-loopsystem can be implemented, where the optical parameters of the transmitside can be tuned to optimally to reflect the current opticalconditions. The tuning parameters include, but not limited to,compensating for aging or environmental effects of optical equipmentfrom the transmitting optical module through to the receiving opticalmodule.

The following description is presented to enable one of ordinary skillin the art to make and use the invention and to incorporate it in thecontext of particular applications. Various modifications, as well as avariety of uses in different applications will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to a wide range of embodiments. Thus, the present inventionis not intended to be limited to the embodiments presented, but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

In the following detailed description, numerous specific details are setforth in order to provide a more thorough understanding of the presentinvention. However, it will be apparent to one skilled in the art thatthe present invention may be practiced without necessarily being limitedto these specific details. In other instances, well-known structures anddevices are shown in block diagram form, rather than in detail, in orderto avoid obscuring the present invention.

The reader's attention is directed to all papers and documents which arefiled concurrently with this specification and which are open to publicinspection with this specification, and the contents of all such papersand documents are incorporated herein by reference. All the featuresdisclosed in this specification, (including any accompanying claims,abstract, and drawings) may be replaced by alternative features servingthe same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

Furthermore, any element in a claim that does not explicitly state“means for” performing a specified function, or “step for” performing aspecific function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph 6. Inparticular, the use of “step of” or “act of” in the Claims herein is notintended to invoke the provisions of 35 U.S.C. 112, Paragraph 6.

Please note, if used, the labels left, right, front, back, top, bottom,forward, reverse, clockwise and counter clockwise have been used forconvenience purposes only and are not intended to imply any particularfixed direction. Instead, they are used to reflect relative locationsand/or directions between various portions of an object.

FIG. 1 is a simplified diagram illustrating optical transceiveraccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 1,transceiver 100 includes an optical receiver 101 that interfaces with anoptical communication link and is configured to receive and processoptical communication signals. In various embodiments, optical receiverincludes various components, such as filter, transimpedance amplifier(TIA), fiber optic connectors, and others. Optical receiver 101 mayadditionally include optical transmission devices such as opticalamplifiers, optical attenuators, chromatic dispersion compensation(static or tunable), lengths of fiber, patch panels and patch cables,optical multiplexers, optical de-multiplexers, etc. Among otherfeatures, optical receiver 101 converts received optical signals toelectrical signals that can later be processed. The electrical signalsare then processed by various digital signal processors (DSP). Forexample, application specific integrated circuit (ASIC) 110 includes FECdecoder 111 and a back-channel detector 112.

It is to be appreciated that once back-channel data are detected fromthe incoming data stream, it is determined that the source of thereceived optical signals is compatible with the use of back-channel datafor adjusting its operating parameters. In various embodiments, the useof back-channel data is a part of a predetermined communication protocolthat two or more transceivers use. If back-channel data is not detectedfrom the received optical signals, the source of the received opticalsignals is not equipped to utilize back-channel data, and it would beunnecessary and even wasteful to perform signal measurements that are tobe embedded into back channel data.

ASIC 110 may also include a module for measuring and analyzing signalintegrity of the received signal (i.e., electrical signals convertedfrom the received optical signals). Signal integrity may be evaluated invarious signal measurements that include, but are not limited to overallsignal-to-noise ratio (SNR), individual PAM-4 level SNR, overall PAM-4histogram, optical eye diagram, and/or others. In additional to signalintegrity, data error rate associated with the incoming signal may beevaluated as well. For example, FEC decoder 111 determines error ratebefore performing error recovery. More specifically, FEC decoder 111 hasthe ability to calculate a bit error ratio (BER) prior to FEC errorrecovery. Depending on the implementation, BER can be calculated inseveral different ways, such as overall BER, individual lane BER,individual PAM-4 level BER (i.e., MSB BER, LSB BER), bit-transitionerror matrix (e.g., in PAM-4, BER for 0→1, 0→2, 0→3 and all other leveltransitions), and/or other ways.

The back-channel detection module 112 is configured to detect whetherthe received signals include back-channel data that can be used tooptimize data transmission performance. For example, the back-channeldata are embedded by the source of the received signals (e.g., anotheroptical transceiver or communication apparatus). In various embodiments,the back-channel detection module 112 is coupled to a control module115. The control module 115 is configured to adjust various operatingand transmission parameters of transceiver 100 based on the back-channeldata. For example, operating parameters include temperature, biassettings, multiplexer settings, wavelength, and others, which aredescribed below. It is to be appreciated that the back-channel detectionmodule 112 may be implemented as a part of the closed feedback loop(e.g., between two optical transceivers). That is, data are transmittedto a second transceiver over an optical communication link. The secondtransceiver includes DSP and FEC module that measure the signal quality(e.g., SNR) and data quality(e.g., BER), and the measurement results areembedded in the back-channel data that are transmitted back totransceiver 100. The back-channel detection module 112 detects theexistence of the back-channel data, which are used by the control module115 to adjust operating parameters of transceiver 100. Depending on theoperating condition and specific implementation, there could beiterations of processes for changing parameters, receiving back-channeldata reflecting the signal quality associated with the changedparameters, and changing parameters again.

It is to be appreciated that, as explained below, back-channel data canbe used to adjust not only transmitter parameters for outgoing data, butalso receiver parameters for processing incoming data. For example, backchannel data can be used to adjust how incoming optical signals areprocessed.

In various embodiments, control module 115 stores near-end parameters,which may be determined at the time when the transceiver 100 ismanufactured. Control module 115 analyzes the received back-channeldata, which reflects the actual conditions of data transmission, and theadjustment of operating parameters can be modifying the existingparameter based on the existing near-end parameters. In variousembodiments, adjustment of operating parameters involves synchronizingand using both existing near-end data and the back-channel data thatreflects conditions for actual data communication.

Transceiver 100 includes an FEC encoder 114 and a back-channel insertionmodule 113 as shown. For example, the FEC encoder 114 and theback-channel insertion module 113 are implemented as a part of the ASIC110. It is to be understood that while FEC decoder 111 and FEC encoder114 are shown as two functional blocks in FIG. 1, FEC decoder 111 andFEC encoder 114 may be implemented a single FEC module. Similarly,back-channel detection module 112 and the back-channel insertion module113 can be implemented as single back-channel module.

FEC encoder 114 is configured to perform FEC encoding for electricalsignals that are to be transmitted through the optical transmitter 102.For example, FEC encoder 114 is configured to perform different types oferror correction. Back-channel insertion module 113 is configured toinsert back-channel data into the outgoing data stream that is to betransmitted. As explained above, back-channel data include informationregarding the quality of received data, which pertains to transmissionparameters and settings of the transmitting transceiver that sends datato transceiver 100. It is to be appreciated that the back-channelinsertion module is capable of inserting and/or detecting, with highfidelity, additional digital information alongside and withoutinterfering with the transmitted data. For example, a predefined segmentof outgoing data stream is used to embed the back-channel data.

In FIG. 1, a close loop technique is used for optical communication,with an optical transmitter and an optical receiver. It is to beunderstood that close loop techniques that use back-channel foroptimizing data communication can be used in other types ofcommunication links as well, such as existing communication lines withcopper wires and/or other mediums.

FIG. 2 is a simplified diagram illustrating an encoded data frameaccording to embodiments of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 2, anexemplary FEC encoded frame can be divided into a most significant bits(MSB) section and a least significant bits (LSB) section. Both the MSBsection and the LSB section include their own respective headers. Forexample, the headers are 128 bits long. A header is then subdivided intoalignment marker region (0-63 bits), “mfas” region (64-71 bits),overhead region (72-120 bits), and “ecc” region (121-127 bits). It is tobe appreciated that overhead region stores back-channel data, whichincludes information related to quality (e.g., measured and/orcalculated) of received signals. For example, an optical transceiverthat is not equipped to take advantage of the back-channel data cansimply ignore and skip over the back-channel region.

Now referring back to FIG. 1. Outgoing electrical signals are convertedto optical signals and transmitted by the optical transmitter 102. Forexample, optical transmitter 102 includes one or more lasers devices(e.g., laser diode with cooling), one or more modulators. Additionally,optical transmitter 102 may include multiplexing and optical controlblocks. Implementation and operating parameters of optical transmitter102 usually have significant impact on signal quality and datatransmission performance of the outgoing data stream. By adjustingoperating parameters and settings of optical transmitter 102, signalquality and data transmission performance can be improved and optimized.While operating parameters and settings can be optimized initially atthe factory, being able to adjust these parameters and settings based onactual signal measurements is better, since actual signal measurementsreflect true operating conditions (e.g., fiber optic lines,interference, temperature, etc.).

According to various embodiments, the control module 115 of thetransceiver 100 processes the received back-channel data, which includeactual measurements of data quality as measured by a second transceiverthat receives data from transceiver 100. The control module 115 thendetermines the optical parameters and settings accordingly. For example,operating parameters and settings may include, but not limited to, thefollowing:

-   -   Laser temperature setting (or TEC current if directly        controlled)    -   Laser bias current    -   Modulator bias setting (e.g., heater power setting if a        thermo-optically controlled MZM)    -   Multiplexer offset bias setting (e.g., heater power setting if a        thermo-optically controlled DLI)

As an example, back-channel data provides signal quality informationthat can be used to adjust parameters of laser devices. Morespecifically, laser devices used for optical data transmission may becontrolled using temperature and bias control parameters. FIG. 3 is asimplified diagram illustrating an optical transmitter with back-channeldata control according to embodiments of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 3, driver301 that generates driver signal based on outgoing data can be adjustedby a voltage swing parameter. Similarly, modulators 302 and 303 may beadjusted using settings such as RF amplitude, DC bias, and/or others.For example, modulators 302 and 303 may be implemented usingMach-Zehnder modulators (MZM). Light source for optical transmitter 300includes laser diodes 305 and 306. For example, laser diodes can beadjusted by changing laser bias and/or laser temperature. Similarly,delay line interferometer (DLI) 304, which functions as an opticalmultiplexer, can be adjusted with an offset bias. It is to beappreciated that the control module 320 of optical transmitter 300 canuse the back-channel data to determine which parameters (as listedabove) are to be adjusted. For example, the control module 320 has acontrol interface that provides control signals for the abovementionedparameters such as bias control, temperature control, swing voltage, andothers.

According to an embodiment, back-channel data are used as a part ofoptical receiver. As an example, optical receiver 101 is a part of thetransceiver 100 as shown in FIG. 1, and various operating parameters ofoptical receiver 101 may be adjusted based on back channel data.

FIG. 4 is a simplified diagram illustrating an optical receiver 400according to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. Optical receiver 400includes polarization beam splitter (PBS) 405 that splits the receivedoptical signal for processing. The received optical signal is thenprocessed by optical multiplexers 403 and 404. For example, multiplexers403 and 404 comprise DLI devices that can be adjusted using biassettings. For thermal-optically controlled DLIs, heater power settingsmay be used to adjust DLI operations. Multiplexers 403 and 404 arecoupled to photodetectors 401 and 402, whose current gain settings canbe adjusted. For example, photodetectors may be amplified, and thus gainsettings are needed. For example, avalanche photodiodes can be adjustedby changing its photocurrent gain. The outputs of photodetectors 401 and402 are coupled to TIA 406, which generates electrical signal based onthe received optical signals. Depending on the implementation, variousparameters such as amplitude, gain, and/or bandwidth, can be adjustedbased on back-channel data. As mentioned above, a control module 420 maybe used to process received back-channel data and generates controlsignals to adjust these parameters.

To make use of back-channel data and to generate control signals forchanging operating parameters, a control module can be used. Forexample, abovementioned control modules 420 may be implemented as a partof a computer engine block, or a microcomputer that is a part of opticaltransceiver ASIC. To use the transceiver 100 as an example, the controlmodule is configured with the back-channel insertion module 113 toinsert digital signals alongside the transmitted optical data, whichdescribe the integrity of the received optical signal (as measured byDSP and/or FEC modules). Additionally, the control module is able to usethe back-channel detector 112 to detect back-channel data embedded inthe received signals. Once detected, the control module processes theback-channel data and generates control signals accordingly. The controlsignals are used to adjust various operating parameters of thetransceiver (e.g., optical receiver, optical transmitter, etc.).Additionally, operating conditions of the optical transceiver may change(e.g., interference, optical line quality, temperature change, etc.). Byusing back-channel data, the control module adjusts and optimizestransceiver performance accordingly. Since the back-channel data areshared between two or more transceivers, two transceivers form afeedback loop for optimizing data transmission over a communicationlink.

In an exemplary embodiment, back-channel data are used to adjust, amongother parameters, transmitting wavelength. In a DWDM system, forexample, the transmitting wavelength is an important parameter. Incertain implementations, transmitting wavelength can be controlled viacarefully tuning the temperature of a thermally tuned laser. However,the actual frequency may not match the measured temperature of thelaser. More specifically, temperature and wavelength for the same laserdevice may change over time as a part of laser device aging process. Asa result, the thermal gradient of a laser device at the beginning oflife calibrations, typically due to aging, becomes inaccurate over anextended period of time. Furthermore, since laser devices generate heat,depending on the packaging and/or placement of the laser device,adjusting laser devices in actual operating condition. For example,thermal gradients are involved with either self-heating or environmentaltemperature interference.

In various embodiments, the control module is positioned on the datatransmission path. For example, the wavelength of the light is measuredusing Fabry-Pérot interferometer (or etalon) type of device. It is to beappreciated that even small changes in frequency and/or wavelength canhave significant impact on the signal integrity of the transmitted data.For example, in various embodiments of the present invention,characteristics of the received signal (e.g., SNR, BER, Eye-Levelparameters, etc.) are passed from a receiving optical transceiver backto the transmitting optical transceiver. The transmitting opticaltransceiver then adjusts the frequency of its one or more lasers andwait for confirmation of whether an improvement has been made, or thesignal has gotten worse, thereby forming a closed feedback loop foroptimizing signal transmission. The transmitting optical transceiver cantry many frequencies (in the right direction) to obtain optimalfrequencies of the one or more lasers.

Below is a simplified process for adjusting optical transceiversaccording to embodiments of the present invention, the process includingthe following steps:

1. At the receiver, measure a bit-error rate BER (“b11”) correspondingto conditions at transmitter temperature setting 1 (“t1”) andtransmitter temperature setting 2 (“t2”), and the receiver uses apredefined back-channel to transmit data back to the transmittingmodule;2. At the transmitting module, modify transmission parameter with stept1 by an amount approximately equal to 0.5 GHz;3. At the receiving module, measure BER (“b21”) and use the back channelto transmit back to the transmitting module;4. At the transmitting module, modify transmission parameter with stept2 by an amount approximately equal to 0.5 GHz;5. At the receiving module, measure BER (“b12”) and use the back channelto transmit back to the transmitting module;6. At the transmitting module, calculate values d1 and d2 (which arechanges to be made to temperature t1 and t2) with the followingequations:d1=g*(1−b21/b11)  ad2=g*(1−b12/b11)  b7. At the transmitting module, adjust t1→t1+d1 and t2→t2+d2; and8. Repeat from step 1 as needed, until an acceptable BER is obtained atthe new t1 and t2 settings.

It is to be noted that steps 1-3 and 4-5 are performed in a changingorder to remove unrelated monotonic effects from the system.

It is to be appreciated the back-channel data can also be used toprovide modulator bias control. Among other things, the bias point ofthe modulator needs to be maintained at the proper value to provide anoptimized extinction ratio. In some cases, the optimal bias point is notat quadrature but rather at a point off-quadrature. Often, a fixed biaspoint is used, which based on for worst-case line system conditions. Invarious embodiments, characteristics of the received signal (includingSNR, BER, Eye-Level parameters, etc.) are measured by the receivingmodule, embedded into back-channel data, and to the transmitting module.The transmitting module adjusts the modulator bias point based on theback-channel data, and waits for indication (embedded in theback-channel data) from the receiving module as a feedback for the nextiteration of adjustment. In this way, the transmitting module cancontinuously seek the optimal modulator bias point until a predeterminedthreshold performance level is obtained.

The back-channel data in closed feedback loop can also be used foradjusting multiplexer bias settings. For example, in a silicon photonicsbased multi-wavelength module design, a delay line interferometer (DLI)may be used to multiplex two optical wavelengths onto the sametransmitting optical fiber. To optimize performance, center frequency ofthe DLI needs to be carefully controlled to optimally pass or separateboth wavelengths.

In an exemplary embodiment, the characteristics of the received signal(e.g., SNR, BER, Eye-Level parameters, etc.) from a transmitting moduleare measured by a receiving module, which inserts the signalcharacteristic information into back-channel data. The back-channel datais then transmitted to the transmitting module, along with other data.The back-channel data is then processed by the transmitting module. Thetransmitting module adjusts the DLI center frequency based on the signalcharacteristics provided in the back-channel data, and transmits data tothe receiving module with new DLI bias setting, and waits for signalcharacteristics information from the receiving module. The feedback loopbetween the transmitting module and the receiving module operates anumber of iterations until certain predetermined conditions are met. Forexample, predetermined conditions may include a predetermined number ofiterations, the total amount of adjustment/calibration time, and/orpredetermined signal characteristics.

In certain embodiments, near-end tuning (e.g., in combination with biassetting) of DLIs are adjusted using the closed-loop back channel data.

Additional parameters and settings of optical transceivers can beadjusted using back-channel data. For example, characteristics of thereceived signal (e.g., SNR, BER, Eye-Level parameters, etc.) aremeasured by a receiving module and inserted to the back-channel data asa part of the closed feedback loop. The transmitting module then usesthe back-channel data to adjust its operating parameters and settings,which include, but not limited, the following:

Modulator swing (RF amplitude);

Laser bias (i.e., Automatic Power Control);

PAM-4 level optimization (in this case the histogram calculated by thereceiver can be used to optimize the level amplitude settings);

PAM-4 MSB/LSB lane skew; and/or

Relative transmitted power among one or more lasers sharing the sameoptical fiber.

For example, by adjusting relative transmitted power among one or morelasers, optical SNR (OSNR) within a channel group can be adjusted tooptimize the overall BER. For example, in a 2-channel 100 G system, thelaunch power and OSNR can be optimized for 100 G BER and still keep thetotal transmitted optical power (CH1+CH2 power) constant.

In certain embodiment, in addition to using the back-channel to transmitdata from the receiving module to the transmitting module, the SNR andBER can be used to optimize near-end parameters, which includes but notlimited to:

TIA output amplitude, gain or bandwidth control;

Photodiode gain (e.g., in an APD); and/or

Receiver de-multiplexer center frequency control (i.e., for a siliconphotonics DLI demux)

In various implementations, two or more parameters of an opticaltransceiver may be adjusted, and when doing so, priority or preferencemay be given to parameters such as far end TX wavelength tuning overnear end RX DLI tuning. For certain parameters, such as far endtransmission MSB/LSB and far PAM 4 swing settings, it may beadvantageous to perform optimization in parallel.

It is to be appreciated that different types of algorithms may beimplemented to take advantage of the feedback mechanisms involvingback-channel data. For example, a transmitting transceiver keepsadjusting its operating parameters based on the measured signalcharacteristics provided by the receiving transceiver until a thresholdlevel of performance is obtained. In certain implementation, opticaltransceivers perform quality continuously and as long as they operate.There are other implementations as well.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. A communication system, the system comprising: acommunication link; a first transceiver comprising a first controlmodule and a first transmitter; and a second transceiver comprising asecond control module and a second transmitter, the second transceiverbeing configured to send data to the first transceiver; wherein: thefirst transceiver is configured to process a first data stream receivedfrom the second transceiver and to detect whether the first data streamcontains a first back channel data, the first back channel data segmentbeing positioned at a predetermined location of an encoded data framefor processing by a compatible device; if the first transceiver detectsthe first back channel data based on a compatibility with the secondtransceiver, the first transceiver is configured to determine signalcharacteristics information associated with the first data stream andinsert the signal characteristic information into a second back channeldata, the second back channel data being embedded in a second datastream; if the first transceiver detects no first back channel data fromthe first data stream, the first transceiver is configured to processthe first data stream without determining the signal characteristicsinformation associated with the first data stream; the secondtransceiver is configured to process the second data stream receivedfrom the first transceiver; and the second transceiver is configured todetect the second back channel data and adjusts one or more operatingparameters based on the signal characteristic information.
 2. The systemof claim 1 wherein the first transceiver further comprises a laserdevice.
 3. The system of claim 2 wherein the operating parameters areused to adjust the laser device.
 4. The system of claim 1 wherein thefirst transceiver further comprises a modulator.
 5. The system of claim1 wherein the first transceiver further comprises a multiplexer.
 6. Thesystem of claim 1 wherein the first transceiver further comprises theforward error correction (FEC) module for determining a bit error rate(BER) associated with the first data stream.
 7. The system of claim 6wherein FEC module is configured to encapsulate the back-channel dataand a portion of the outgoing data stream into an FEC frame.
 8. Thesystem of claim 1 wherein the first control module is configured forgenerating the first backchannel data.
 9. The system of claim 8 whereinthe backchannel data are posited at a predetermined location of anencoded data frame for comprising by a compatible device.
 10. The systemof claim 9 wherein the compatible device includes the secondtransceiver.
 11. The system of claim 1 wherein the second transceivercomprises an optical transmitter.
 12. The system of claim 1 wherein thefirst transceiver comprises a digital signal processor configured todetermine the signal characteristic information.
 13. The system of claim12 wherein the signal characteristic information comprises asignal-to-noise ratio.
 14. An optical transceiver apparatus comprising:a receiver for receiving an incoming data stream from a communicationapparatus; a detection module configured to detect first back-channeldata from the incoming data stream based on a compatibility with thecommunication apparatus; a digital signal processor (DSP) configured toanalyze the incoming data stream and to generate a first signal qualityvalue characterizing the incoming data stream if the incoming datastream is compatible; a forward-error correction (FEC) module configuredto process the incoming data stream and to generate a second signalquality value characterizing an error rate associated with the incomingdata stream if the incoming data stream is compatible; a control moduleconfigured to, when the incoming data stream is compatible: generatesecond back-channel data based at least on the first signal qualityvalue and the second signal quality value; and insert the secondback-channel data to an outgoing data stream, the second back-channeldata being positioned at a predetermined location of an encoded dataframe for processing by a compatible device; and a transmitter foroutputting the outgoing data stream.
 15. The apparatus of claim 14wherein the transmitter comprises an optical transmitter for generatingoutput optical signals based on the outgoing data stream.
 16. Theapparatus of claim 14 wherein the receiver comprises an optical receiverfor converting incoming optical signals to the incoming data stream. 17.The apparatus of claim 14 wherein the incoming data stream compriseselectrical signals.
 18. A method for optimizing optical communication,the method comprising: transmitting a first data stream from a firstoptical transceiver to a second optical transceiver via an opticalcommunication link; detecting a first back-channel data segment at thefirst data stream by the second optical transceiver based on acompatibility with the first optical transceiver, the first back-channeldata segment being positioned at a predetermined location of an encodeddata frame for processing by a compatible device; determining a firstset of measurements associated with the first data stream by the secondoptical transceiver if the first back-channel data segment iscompatible; generating a second back-channel data by the second opticaltransceiver, if the first back-channel data segment is compatible, thesecond back-channel data comprising the first set of measurements, thefirst set of measurements including a first signal quality valueassociated with electrical signals and a second signal quality valueassociated with an error rate of the electrical signals; inserting thesecond back-channel data to a second data stream by the second opticaltransceiver if the first back-channel data segment is compatible;transmitting the second data stream from the second optical transceiverto the first optical transceiver; detecting the second back-channel databy the first optical transceiver; determining a first set of adjustmentsby the first optical transceiver based on the first set of measurements;and applying the first set of adjustments to an optical transmitter bythe first optical transceiver.
 19. The method of claim 18 furthercomprising: transmitting a third data stream in accordance to the firstset of adjustments from the first optical transceiver to the secondoptical transceiver; determining a second set of measurements associatedwith the third data stream by the second optical transceiver; andgenerating a third back-channel data by the second optical transceiver,the third back-channel data comprising the second set of measurements.20. The method of claim 19 further comprising: inserting the thirdback-channel data to a fourth data stream by the second opticaltransceiver; transmitting the fourth data stream from the second opticaltransceiver to the first optical transceiver; processing the fourth datastream by the first optical transceiver; and determining a second set ofadjustments by the first optical transceiver based on the second set ofmeasurements.